Signal-generating system



A. v.' LOUGHREN 2,396,865

SIGNAL-GENERATING SYSTEM Filed March zo, 194s 2 sheets-sheet 1 Mafch 19,1945.

March 19, 1946. A V, LOUGHREN- 2,396,865

SIGNAL-GENERATING SYSTEM Filed March 50, 1943 2 Sheets-Sheet 2 FIGB 'UMMILMWUUULVUUUMWWWWUU FIG-4- INVENTOR ARTHUR V. LOUGHREN Patenied Mar.19, 1946 .UNITEDv STATES PATENT :o1-FICE- y SIGNAL-GENERATING SYSTEM vArthur V. Longhi-en, Great Neck, N. Y.. assigner to HazeltineCorporation, a corporationot Deb aware Application March 30, 1943,Serial No. 481,104

15 Claims.

This invention relates to signal-generating systems and is particularlydirected to the reduction oi undesirable shading signals which aregenery ally produced along with the desired signal components in thosegenerating systems that utilize a camera tube as the signal generator.While the invention has a wide range of application, it is especiallyysuited to television signal-generating systems, and in the descriptionwhich follows, its apllication to suh ay system is described indeta Inay television signalvgenerating system oi the type under consideration,the camera tube may comprisea cathode-ray tube having aphotosensitivemosaic target electrode, an electron gun for developing,accelerating and focusing anelectron beam on the target electrode, andmeans for scanning the target with the beam duringsuccessive scanningintervals. In such an arrangementan optical system establishes a chargedistribution on the target electrode in accordance with an image to betranslated so that during the scanning operation video-frequency signalcomponents corresponding to the image are produced in the output circuitof the tube. It has been lfound, however, that undesired spurioussignals, commonly referred to as' shading components; are v alsoproduced duringthe scanning operation along' with the desiredvideo-frequency signal components. If suchspuriQuS Signals ,arenas-remiwed. they' causellndesrblefshading in the reprbdug' ',fimage, n Y. p

In order l to`eliminate` `or effectively reduce 'the undesired shading"signals v studies 1 have been: made to determine their cause'.l Thesestudies revealed that, during the scanning operation, secondaryelectrons are emitted from the target elec- Atrode and thereturn'if'rain-back of' these secn ondary electrons to the targetproduces a current which is one component of-the shadingsignal,

Since this phenomenon is produced by thescanning operation, the shadingsignal has compo- -nents which correspond infrequen'cy to the scan'-ning frequencies. It has been proposed, there,-

.Ifore, tominimize vthese shading components by .l inserting a suitableand artificial compensating signal in the video-frequency signal which`is derived from the cathode-ray signal-generating tube. It'has beenfound thatv such an articia-l signal having a saw-tooth, exponential, orparaj' bolic lwave form and having frequency compofnent's related to one0r both 0f the Scanning tre:

quencies of the camera tube may, insome cases, -be effective tol reducethe shading signal to a limited extent. This method of compensation,how- (ci. iva-1.2) A' ever, has the disadvantage-that itfrequireselaborate and expensive equipment which is both difcult and inconvenientto operate successfully the loss of desired video-frequency componentsinvolves the use of a line raster or grid in the optical system, or anequivalent arrangement for 2l) causing the optical image on thetargetelectrodeto be broken up or. for'causingjthe lines oi the l ltarget ,electrode tofhave alternately exposed and y unexposed elementaryareas. vWhen the (electron beam .isf incident yupon an exposedelementary 25 area of the'gtarget electrode in such anarrangeexpQedelementar-y jarea, vthe output 3 0 sista solely. of shadingcomponents.-A

' nin'gftheesuccessivelyexposed elementary'areas the image isto bereproduced without impairment and furthe arrangement to-be operable,.the scanning 4spot must be ofy neness comparable, nottdthe'tele'v'isionimage structure..but to the 45; structure er the une raster. Presenttechniques where this requirement can be readily met so `that sucharrangements have limited'practical value.

It is anobject of the present invention, there-l fore, to provide animproved signalfgenerating system which'avoidsone or more of the above'-mentioned disadvantages of the prior art arrangements. It is another 55ia signal-generating system having an improved ment, the`joutput signalconsists of video-ffre-.xv quency-signalecomponents and shading compovnents'butwhenthe beam is incident upon anvjun-"z signalconv- Means areprovided-@for deriving as e useful-signal rthe difev ference' betweenthe signals obtained when scanthefvunexposed elementary v areas.Y While.

:35 such lan-Iarrangement represents what is believed,

to'betheproper approach to shading component 'vcorrectilitfisgsubjecteto Acertain limitations.- 11twill-bev understoodthat theline raster must have l an appreciablm ilnei` structure than -l,the struc-I l 40 ture of thetelevision image .to be translated if inelectron optics have, not advanced to astage object ofthe invention toprovide in the description of the erating system comprises, acathode-ray signaly l generating tube, a photosensitive target electroden the tube, means for establishing a charge distribution on the targetelectrode in accordance with a signal to be generated, a source of beamcurrent in the tube, and means for scanning the Vtarget electrode duringa scanning interval with the beam to generate desired signal componentshaving frequencies that extend over a range de- For a betterunderstanding oi' the present invention, together with other and furtherobjects thereof, reference is had to the following description taken inconnection withthe accompanying drawings, and its scope will be pointedout in the appended claims.

,In the accompanying drawings, Fig. 1 is a circuit diagram, partlyschematic.. of a complete television signal-generating .andtransmittingl system embodying the present. invention: Figs. 2 to 7,inclusive, comprise curves used as an aid generating system of Fig. 1;Fig. 8 is a circuit diagram of a modification of a portion of the systemof Fig. 1; and Fig.

9 comprises curves used as anaid in describing the operation of thecircuit arrangement of Fig. 8.

Referring now more particularly to Fig. 1 ot the drawings, thetelevision signal-generating and transmitting system illustratedcomprises a cathode-ray signal-generating tube I5 having aphotosensitive mosaic target electrode i6, a

termined by the charge distribution on the target electrode and whichalso develops undesired shading components with the desired signalcomponents. The system includes additional means for periodically andsubstantially decreasing the current of the beam from a predeterminedvalue during the scanning interval at a frequency which is at least ashigh nal component generated, and frequency-responsive means coupled tothe tube having a frequency characteristic related .to the frequency atwhich the beam current is decreased for deriving a signal which includesthe desired signal components and which is substantially free ofundesired shading components.

In accordance with a preferred embodiment of the invention, the beamcurrent of-a cathode-ray type signal-generating tube is periodicallyinterrupted during the scanning of the target electrode, theinterruption frequency being high compared with the highestvideo-frequency signal component generated. During intervals when theelectron beam isincident upon the target electrode, the signal producedin thetube includes both desired video-frequency signal components andundesired shading components. During intervals when the beam isinterrupted, however, the signal produced comprises only undesiredshading components. Stabilizing means coupled tothe output circuit ofthe tube derive a signal which effectively comprises the diii'erencebetween the signals produced when the beam is incident upon the targetelectrode and when the beam is interrupted. Consequently, `the derivedsignal includes the desired video-frequency signal y components andissubstantially free of the undesired shading components.

In accordance with another embodiment of the invention, means includinga band-pass lter are coupled to the output circuit of the cathode-raysignal-generating tube for deriving therefrom a signal which includesdesired video -i'requency signal components and which is substantiallyfree ofundesired shading components. In this arrangement, advantage istaken of the fact that the periodic interruption of the beam current ata rate which is high compared with thehighest video-frequency signalcomponent generated .produces a carrier signal modulated only by the asthe highest-frequency sig- 4 desired video-frequency Signal components.The r band-pass lter of this arrangement is Adeslilrneeis to select thecarrier signal and one or bgth of its f sidebands of modulation.

.source of beam current including anlelectron gun structure as well asfocusing and accelerating electrodes lto which suitable operatingpotentials are supplied from a source Il, beam-deiiecting elements I8,AI8 and an output circuit including a load impedance 20. An opticalmeans I4 is provided for establishing a charge distribution on thetarget electrode in accordance with an image to be transmitted.

VConnected in cascade to the load impedance 2li of signal generator l5,in the order named, are a signal-translating unit 33 to be described indetail hereinafter, a combining amplifier 2|, a modulator 22 and anassociated carrier-frequency oscillator 23, a power ampliiler 24, and aradiating antenna system 25, 26. Deilecting voltages of saw-tooth waveform are supplied to deflecting elements I8, I9 from outputcircuits oi'a. linescanning generator 21 and a field-scanning generator 28,respectively, to cause the beam of signal-generating tube l5 to scan thetarget electrode in a series of elds oi parallel lines. Blockoutvoltagesv are supplied from generator 28 through a blocking condenser 60to a control electrode 38 of tube l5 to suppress the beam during retracescanning intervals. Output circuits of generators 21, 28, 28 are coupledto combining amplifier 2l to supply thereto synchronizing signals andblock-'out signals for transmissionwith the radiated carrier wave. Thesegenerators are synchronized by timing pulses from timing-impulsegenerator -30 which is preferably stabilized by means of a connection 3ito a suitable source of periodic voltage, for example,v to thepowersupply circuit or to the synchronizing-voltage source of motionpicture mechanism where such is employed. A high-frequency generator 22of conventional design produces a control potential whicn isappliedtothe control electrode of tube i5 for a purpose to be described morefully hereinafter.

Neglecting for the moment the' functions of units I2 and 33, thev systemAjust described comprises the elements of a television signal-generatingand transmitting'system of conventional design and, since the variouselements I4 to 2i, inclusive, thereof may be of any well-knownconstruction, a detailed description ot the general systemand itsoperation is unnecessary. Brie'ily, however, the image of a. scene to betransmitted is focused on., the target electrode i6 in signal-'generator tube Il and video-frequency signal components havingamplitudes and frequencies aandoet that extend over a range determined.by the motion be at leasttwice as'nign as the highest charge;distribution on the target electrode and v'the' scanning frequencies aredeveloped-across vload impedance 20 in the usual manner and are appliedthrough unit 33 to vcox'nlziinin amplier synchronizing-signal andblock-out signal components from generators 21, 28 and 23 areV alsoapplied to amplifier 2| in which they are mixed with the video-frequencysignal componentsand amplified. The amplied composite signal is suppliedto modulator 22 where itis so impressed upon the carrier wave generatedby oscillator 23 as to develop a modulated-carrier i signal. This signalis delivered to power amplier 24 for amplification therein and isthereafter impressed upon antenna system 25, 25 to be radiated. v

The signal appearing acrossvload impedance 20 of signal generator I whenthe generator is utilized in a conventional televisionsignal-transmitting system of the type just described will be considerednow more particularly. As is well un derstood, the photosensitiveelements of target video-frequency 4signal componentv lgenerated and, inparticular, it is desirable that the period of interruption be shortcompared with the average transit'time-of the returning secondaryelectrons.. The curve of Fig. 4 representsthe variations in beamcurrentduring thel scanning'interval in response to .this-controlpotential.A `It will be seen that the beam current is periodically 1video-frequency signal components and undeelectrode i6 acquire chargesdependent upon the varying values of light in the correspondingelemental areas of the image focused thereon by the optical system M.The curve of Fig. 2 is assumed to represent such a charge distributionfor a portion of a single scanning line on the target electrode. In thisgure, rzero value of charge represents the white level inthe imagefocused on the target and a charge value of -Ci vrepresents the blacklevel in that image. The polarities of the ordinate axis have beenassigned in a manner opposite to conventional practice in order tofacilitate a comparison of the charge-distribution curve with curves, tobe discussed hereinafter, representing the generated signal. When thisline portion is scanned with ay cathode-ray beam, video-frequency signalcomponents are produced in the output circuit of the generator. At thesame time, however, secondary electrons emitted from the targetelectrode during the scanning operation rain back thereon and thiselectron movement develops the above-mentioned undesired shadingcomponents which also appear in the output circuit of the generator.Consequently, the signal produced across load impedance 20 'under theassumed condition may be as represented by the curve of Fig. 3. Acomparivson of this curve with that of Fig. 2 shows that the undesiredshading components are represented by the general slope of the curve ofFig. 3. If this slope is reduced to substantially zero value, theundesired shading components are removed and the resultant signalcontains only the desired video-frequency signal components.

' This result is obtained, in accordance with the` decreased from anormal. predetermined value Ii to substantially zero value, indicatedIn.

When the'line portion o! target velectrode I6 having the chargedistribution' represented by the curve of. Fig. 2 is scanned with theperiodically vinterrupted beam, a signal is'developed across loadimpedance 2liA in the output circuit ofv .thegenerator as represented bythe curve of Fig.

5. The general slope of this curve is again assuxned to be produced bythe undesired shading components. Hence, it will be seen .that theinstantaneous value e1' of signal voltage obtained when the beam.isenergized includes desired sired shading components, while theinstantaneous value es of signal voltage obtainedduring intervals whenthe beam is interrupted consists only of vundesired shading components.Unit 33 is coupled to load impedance 20 for selecting, as a signal fortransmission, the diierence between signal values er and e2 which recurin alternation during any scanning interval.

This unit comprises a videofrequency amplifier 38 having an inputcircuit coupled across load impedance 20 and an output circuit to whichis connected a signal-stabilizing means-including Y a diode rectiiler35, coupling condenser 36and' load resistor 31. Amplier 34 is selected-to have a .substantially flat frequency-response characteristic for arange of frequencies including. the desired' video-frequency componentsIshading l components, and interruption-frequency compresent invention,through the addition oli-units '32 and 33 to the generating system.

. Unit 32 comprises means for periodically and I ysubstantiallydecreasing the current of the beam in vgenerator l5 `from apredetermined, value, or

the value which it would normally have during; the scanning interval, ata Afrequency which -is at least as high as the highest video-frequencysignal component produced in the generator. In accordance with apreferred embodiment of the invention this unit'delivers to control grid38- of generator l5 a control potential havinga substantiallyrectangular pulse waveform and of such value that the beam current ofthe -ger'i- -erator is periodically interrupted Aeluring the' scanningof each line of the target electrode; Also, it is preferred that thefrequency of interl ponents so that the signal from generator l5 vmay betranslated .therethrough without distortion. Further, in order toystabilize this signal,

the values of condenser 36 and resistor 31 are so chosen as to give thesignal-stabilizing means a time constant which is long'compared with theperiod of vinterruption of the beam current and short compared with theline-scanning period of the signal generator.

m considering the operation of unit sa, it win be seen that thecomposite signal produced across load 4impedance 23 of generator I5which includes desired video-frequency signal components and undesiredshading components is applied to the input terminals of amplifier 34and, after amplification therein, appears at the output terminals withreversed polarity and Asuperimposed on the direct current Asignalcomponent of the amplier asindicated` by the curve of Fig. 6, Thisamplified signal is peak-rectied in diode 35 and, due to the long timeconstant of condenser 36 and resistor 31, is effectively stabilized onits' positive peaks. That is, these peaks of the sig- -nal are alignedat' a fixed potential level, as indicated by the curve of Fig. '1,whereby the general slope of the curve which has been assumed torepresent the `shading components is'reduced to a zero value. It will beclear upon a comparison of the curves of Figs. 2 and '1 that the signalthus applied to combining amplifier 2l for transv mission includesthe'desired video-frequency sign al components and is substantiallyvfreeof the undesired shading components.

Since the time' constant ofthe stabilizing circuit is proportioned withrespect to the period `at control potential of sinusoidal wave form. Inksuch `case also, the generating which the beam current is interrupted,unit 33 comprises frequency-responsive means coupled to tube IB having afrequency characteristic related to the frequency at which the beamcurrent is decreased or interrupted for deriving a signal which inducesthe desired signal compo-r nents and which is substantially free Vofundesired shading components.

The described operation of unit 33 in removing the undesired shadingcomponents from the generated signal may be considered from a slightlydiifer'ent view. The signal voltages developed by the camera tube underthe inuence -of the scanning beam are inversely related to the values ofincident light in the `image focused on the targetl electrode. In otherwords. small values of signal voltage are obtained during the scanningof those portions of the target electrode that are brilliantlyilluminated, while large values' of signal voltage are obtained duringthe scanning of asados l tentials are supplied from sources indicated as+B and Se. The described amplifier arrangement may be substituted forvideo-frequencyl amplifier 34 in the television system of Fig. 1 forselecting the modulated carrier wave from the output circuit of thegenerator. After amplification, this wave is applied to diode 35 whereits modulation components are derived and delivered tb combiningamplifier 2l for transmission.

This modified form of the invention operates by virtue of the fact thata carrier wave modulated by the desired video-frequency signalcomponents is produced ,across loadv impedance when the beam current ofgenerator I5 is periodically interrupted at a carrier-frequency rateduring the scanning interval. The carrier frequency of this modulatedwave is equal to the frequency of beam current interruption so that thedarker portions of .the target. Accordingly,

when the beamcurrent is interrupted, the sig'- nal obtained from thegenerator should represent an absolute level of picture brightnesscomparable to the white level. Therefore, the periodic interruption ofthe beam current .effectively produces recurrent signal componentshaving a predetermined datum level corresponding to the white level ofthe image to be transmitted. Unit 33 in stabilizing the generated signalestablishes the recurrent signal level which represents an absolutelevel of incident light at a xed potential and thus removes theundesired shading components.

In the'foregoing description of a preferred embodimentof the inventionit was stated that the beam current control potential supplied bygenerator 32 should have a substantially rectangular pulse wave form. Itis well known that vsignals of such wave form are rich in harmonicswhereby a wide pass band is required to translateA them withoutdistortion. 'I'he pass band requirement maybe reduced considerably -byutilizing a or other suitable system of Fig. 1 operates substantially asdescribed to ldevelop a` television signal which includes the desiredvideo-frequency components but which is substantially free ofundesiredshading components.

In Fig. 8 there is disclosed a modification of the frequency-responsivemeans which is coupled to generator Isin accordance with the presentinvention for deriving a signal that includes comprising a transformerv4 5 double-tuned by condensers Il, included in its output circuit. Eachi'llter section is tuned to the carrier frequency of a modulated carrierwave which, as

' will be described presently, is developed across the load impedance.2l of signal generator I5.

A self-biasing arrangement consisting of a resistor 5t, by-passed.. forhigh-frequency signals bycondenser 5l, is provided in accordance withconventional practice and suitable operating-porange from 0 to fr andinclude desired video-fre if the interruption frequency is at leasttwice as high as the highest video-frequency signal' componentgeneratedfupper and lower sidebands of modulation componentsindividually representing the desired video-frequency signal componentsare produced and may be readily selected from the output circuit of thegenerator through a bandpass filter arrangement of the type justdescribed. The undesired shading components do not appear as modulationon the carrier wave since the shading signal has substantially the samevalue during intervals when the beam is effective and sucneedingintervals when the beam current is interrupted so long as the period ofinterruption is high compared with the average transit time of thereturning secondary electrons.

'.An operating characteristic of the arrangement of Fig. 1, assuming theradio-frequency amplifier of Fig. 8 to have been susbtituted for thevideo- 'frequency amplier 34, is disclosedin Fig. 9 where broken-linecurve A represents the signal components generated in tube I5 during ascanning interval if the beam current is not interrupted.v

'I'hese signal components extend over a frequency quency signalcomponents and undesired shading components. The operating frequency fzof generator 32 is considered to be adjusted to a value which is greaterthan twice that of frequency f1 corresponding to the highestvideo-freist quency signal component generated. Accordingly. themodulated carrier wave available in the output circuit of the generator,as illustrated by curve B of Fig. 9, comprises a carrier-wave componenthaving a carrier frequency fz, a lower sideband of modulation componentsextending over the'frequency range fa-h, and an upper sideband ofmodulation components extending over the frequency range .f2-f4. thesidebands of modu. lation individually representing the desiredvideofrequency components. Since the modulated carrier wave is spaced inthe frequency spectrum from the range O-ji, it may be readily selectedto the exclusion of shading components by adjusting the tuned circuitsof the radio-frequency amplier to have a mean operating frequency f2 anda pass band corresponding to the frequency range fs-fl. If necessary,damping resistors may be added to the tuned circuits in well-known Ymanner to obtain the required frequency range for the lter circuits.These resistors are indicated in dotted construction in Fig. 8 sincethey may be comprised in part or in whole of the inherent resistances ofthe tuned circuits. After amplication in the radio-frequency amplifier,the modulated wave is applied to diode 3'5 where its modulationcomponents which represent the desired Vshading components. thenbeapplied to diode 'may be transmitted directly Vassesses componentsderived at theutilizingapparatus, all

-as aforedescribed. v f t K 7It.will alsobe' understood that generator32 need not necessarily be operated at afixed frej video-frequencycomponents are derived and supplied to combining amplier 2| fortransmission in `a conventional manner.

Thus in the described'modiflcation of the invention, cooperation withthe quency-responsive means coupled to tube l having a frequencycharacteristic related to the frequency at which the beam'current isdecreased or interrupted for deriving a signal for transmistheradio-frequency amplifier of Fig. s in diode 35 comprises fre-l sionwhich comprises the modulation components l of the modulated-carriersignal developed in the tube and which is substantially freeof undesiredshading components.

In certain applications it may be desirable to transmit the carrier wavemodulated with the I desired video-frequency components and to derivethe modulation components by detection in the usual manner at thereceivervorutilizing apparatus. In such instances a radio-frequencyampliilerof the type disclosed in Fig. 8 may be coupled to the loadimpedance of tube |5.` The pass-band characteristics ofthe amplier areto be chosen in the manner already described so that the amplifiercomprises frequency-responsivemeans coupled to ,the tube having afrequency characteristic related tothe frequency at whichthe beamcurrent is decreased or interrupted for deriving a signal whichcomprises the modulated carrier wave and which is .substantially free ofundesired shading components. The modulated carrier wave, afteramplication, may be applied directly to an antenna system 'or it may be.applied to a frequency changer and heterodyned toa frequency moresuitable for radiation. In these applications the necessarysynchronizing signals may be conveniently transmitted to the utilizingapparatus by way of a separate channel or carrier wave.

It will be understood that it is not necessary to select both sidebandsof modulation components quency operation of I While there-havebee'ndescribedwhat are at skilled inthe art since the entire range ofvideo-frequency signal components is included within either one.Therefore, the radio-frequencyamplifier may be adjusted, if desired, toselect only one of the sidebands of modulation. It will'also beunderstood that the pass band of theamplifier need only be sufficientlywide to select those sideband com` ponents that represent thevideo-frequency-signal components which the associated apparatus iscapable of utilizing. In other words. even when transmitting a singlesideband of modulation components, it will not be necessary to transmitAal1 the modulation components if., the receiving apparatus is able toutilize only a limited portion of the video-frequency -signalcomponents'produced in-the generator 15. Accordingly the phrase"desired'signal components asemployed.

f :throughout this description and in the appended f claims is intendedto mean the signal components desired for'u'tilization.

Furthenuit maybe seen that generator '3 2 may l be operated atavfrequency comparable to that of the highest video-frequency signalcomponent to 'l be generated. Inf such a case, however, it is necessarylto adjust the tuned circuits of the radiofrequency amplifier to selecttheuppersideband #fof modulation components in order to obtain a signalwhich is substantially free of undesired The selected signal maycomponents are derived and supplied tofcomloining amplier 2l fortransmission,

and its modulation 35 where its modulation' or the signal quency sincetheinterruption frequency may vary over a considerable range withoutadversely affecting the operation of the system. ,Accordingly, thephrase .means for periodically and substantiahy decreasing the ycurrentlof :the beam and similar expressions used'in the foregoingr de.lscription and 'in the appended' vclaims is intended to include bothfixed-frequency and variable-frethis generator.

present` considered tofbe the preferredemb'odiy.ments of this invention,

that' various changesandmodiflcations :may be made ,threinwithoutdeparting from the invention, and it is, therefore', aimed in theappended claims to cover all such changes and modifications as fallwithin the true spirit andscope of theinvention. l' i Whatis claimed is:

erating ,systemy comprising, a

l. A signal-ge' cathode-ray sig al-generating tube, aphotosensitivejtarget electrodel in -said tube', means for' establishinga charge distribution on said target electrode in accordance with asignal Ate be gen- `erated, a source of be'am current in said tube,

`means for scannings'aid target electrode duringk a scanning intervalwith said beam to generateA desired signal components having frequenciesthat extend over a range determined by the charge distribution on saidtarget electrode andA which also develops undesired'shading componentswith said desired components, means for periodically and substantiallydecreasing thevcurrent of saidjbeam from a predetermined value duringsaid scanning interval at a frequency which is at least as high as thehighest-frequency signal component generated, and frequency-responsivemeans coupled to said tube having a frequency characteristic related tothe frequency at which said beam lcurrent is decreased for deriving asignal which' includes said desired signal components and .which is sub-`tantia1ly`free of said undesired shading com-.

ponents. j

2. A signal-generating system comprising, a

' cathode -ray signal-generating tube, a photosensitive target electrodein said tubetmeans for establishing a charge distribution on said targetelectrode in accordance` with a signal to b e generated,

'a source of beam current in said tube, means for scanning said targetelectrode during a scanning interval with said -bcam to generate desiredsignal components having frequencies that extendl over a rangedetermined by the charge distribution on said target -electrode andWhichalso 'develops undesired shading components with said y -I ydesired components, .means `for periodically andsubstantially decreasingthecurrent of said beam from a predetermined value during said scanningsaid beam current is decreased for deriving a siginterval at a fixed`frequency which is at least as high as the vhighest-frequencysignal'com--' and frequency-responsive v ponent generated, means coupledto said tube having a frequency characteristic related to the frequencyat which nal which includes said desired signal components and which issubstantially free of said undesired shading components.

l3; A signal-generating ysystem comprising, a

.cathode-.ray signal-generating tube, a photosensitive'target electrodein said tube, means for establishing a charge distribution on saidtarget 4elecit will be obvious to those fated', a for scanning saidtarget electrode during a scantrode in accordance with a signal to begenerated, a source of beam current in said tube, means for scanningsaid target electrode during a scanning interval with said beam togenerate desired signal components having frequencies that extend over arange determined by the charge distribu- `tion on said target electrodeand which also develops undesired shading components with saiddesiredcomponents, means for periodically and substantially decreasing thecurrent of said beam from a predetermined value during said scanninginterval at a frequency which is atleast twice as high as thehighest-frequency signal component generated, and frequency-responsivemeans coupled tosaid tube having a frequency characteristic related tothe frequency at which said beam current is decreased for deriving asignalV which includes -said desired signal components and which issubstantially free of said undesired shading components.

4. A signal-generating system comprising, a cathode-raysignal-generating tube, a, photosensitive target electrode in said tube,means for establishing a charge distribution on said target electrode inaccordance with a signal to be genersource of beam current in said tube,means ning interval with said beam to generate desired signalcomponentshaving frequencies that extend over a range determined bythecharge distribution on said target electrode and which also developsundesired shading components with said desired components, means forperiodically interrupting the current of said beam during said scanninginterval at a frequency which is at least as high as thehighest-frequency signal component generated, and frequency-responsivemeans coupled to said tube having a frequency characteristic related tothe frequency at which said beam current is interrupted for-deriving asignal -which includes said desired signal components and which issubstantially free of said undesired shading components.

5. A television signal-generating system comprising, a cathode-raysignal-generating tube. a photosen'sitive target electrode in said tube,means for establishing a charge distribution on said target electrode inaccordance with an image to -be generated, a source of beam current insaid tube, means for scanning said target electrode during a scanninginterval with said beam to generate detrode during a scanning intervalwith said beam ,u

to generate desired signal components having frequencies that extendover a range determined by the charge distribution on said targetelectrode and which also develops undesired shading components with saiddesired components, means for applying to said control electrode acontrol potential for periodically and substantially decreasing thecurrent of said beam from a predetermined value during said scanninginterval at a frequency which is at leastas high as thehighest-frequency signal component generated, and frequency-responsivemeans coupled to said tube having a frequency characteristic related tothe frequency at which said beam current is a signal which includes saiddesired signal components and which is substantially free of saidundesired shading components.

7. VA signal-generating system comprising, a

cathode-ray signal-generating tube having a control electrode, aphotosensitive target electrode in said tube, means for establishing acharge distribution on said target electrode in accordance with a signalto be generated, a source of beam current in said tube, means forscanning said target electrode during a scanning interval with said beamto generate desired signal components having frequencies that extendover a range determined by the charge condition of said target electrodeand which also develops undesired shading components with said desiredcomponents, means for applying to said control electrode a controlpotential having a rectangular-pulse wave form for sired video-frequencysignal components having frequencies that extend over a range determinedby the charge distribution on said target electrode and which alsodevelops undesired shadingA components with said desired-components,means for periodically and lsubstantially decreasing the current of saidbeam from a predetermined value during said scanning interval at afrequency which is at leasthas high as the highest videofrequency signalcomponent generated, and frequency-responsive means coupled to said tubehaving a frequency characteristic related to the frequency at which saidbeam current is decreased for deriving a signal which includes saiddesired video-frequency signal components and which is substantiallyfree of said undesired shading components. y

6. A signal-generating system comprising, a cathode-raysignal-generating tube having a control electrode, a. photosensitivetarget electrode in said tube, means for establishing a chargedistribution on said target electrode in accordance with a. signal to begenerated, a source of beam current in said tube, means for. scanningsaid target elecperiodically and substantially decreasing the current ofsaid beam from a predetermined value during said scanning interval at afrequency which is at least as high as the highest-frequency signalcomponentl generated, and frequency-responsive means coupled to saidtube having a frequency characteristic related to the frequency at whichsaid beam current is decreased for deriving a signal which includes saiddesired signal components and which is substantially free of saidundesired shading components. i

8. A signal-generating system comprising, a cathode-raysignal-generating tube having a control electrode, a photosensitivetarget electrode in said tube, means for establishing a chargedistribution on said target electrode in accordance with a signal to begenerated, a source of beam current in said tube, means for scanningsaid target electrode during a scanning interval with said beam togenerate desired signal components having frequencies that extend over arange determined by the charge distribution on said target electrode andwhich also develops undesired shading components with said desiredcomponents, means including a high-frequencyl generator for applying tosaid control electrode a control potential for periodically andsubstantially decreasing the current of said beam from a predeterminedvalue during said scanning interval at a frequency which is at least ashigh as the highest-frequency signal component generated, andfrequency-responsive means coupled to said tube having a frequencycharacteristic related to the frequency. at which said beam current isdecreased for deriving a signal which includes said desired signalcoinponents and which is substantially free of said undesired shadingcomponents.

.9. A signal-generating system comprising,4 a cathode-raysignal-generating tube, a photosensitlve target electrodeI in said tube,means for establishing a charge distribution on said target electrode inaccordance with a signal to be generdecreased for deriving y ninginterval with said beam ated, a source of beam current in said tube,means for scanning said'target electrode during a scani to generatedesired signal components having tribution on said target electrode andwhich also develops undesired shading components with said desiredcomponents, means for periodicallyand substantially interrupting thecurrent of said beam during said scanning interval at a frequency whichis at least as high as the highest-frequency signal component generated,and peak-rectifying means coupled to said tube having a time-constantwhich is long with respect to theperiod of' said interruption frequencyfor deriving a signal which includes said desired signal components andwhich is substantially free of said undesired Shad-- ing components.

10. A signal-generating system comprising, a

cathode-ray signal-generating tube, a photosensitive target electrode insaidl tube, means for establishing a charge distribution on said targetelectrode in accordance with a signal to be generated, a source of beamcurrent in said tube, means substantially interrupting the currentofsaidk beam during said scanning interval at a frequency which is atleast as high as the highest-frequency signal component generated toproduce recurrent signal components having a predetermined datum level,and means coupled to said tube having a frequency characteristic relatedto the frequency at which said beam 'is interrupted for stabilizing saidlast-named signal components at a fixed signal level to derive a signalwhich includes said frequencies that extend over'a range determined bythe charge disdesired signal components and which is substanv tiallyfree of said undesired shading components.

l1. A television signal-generating system comprising, a cathode-raysignal-generating tube, a photosensitive target electrode in said tube,means for establishing a charge distribution on said target .electrodein accordance with an image tob generated, a source of beam current insaid tube, means for scanning said target electrode during a scanninginterval with said beam to generate desired video-frequency signalcomponents having frequencies that extend over a range deter- `mined bythe charge distribution on said target electrode and which also developsundesired shadrupting the current of said beam during said l scanninginterval at a frequency which is at least as high as the highestvideo-frequency signal component generated to produce recurrent signalcomponents having a datum level correspondingfrequency signal componenty a carrier signal modulated by said desired signal components, andfrequency-responsive means t yteristic related v tion components.

electrode in accordance with' a signal to be generated, a source of beamcurrent in said tube, means for scanning said target electrode during ascanning interval with said beam Ato generate desired signal componentshaving frequencies that extend over a range dition ofsaid targetelectrode and which also develops undesired shading components with saiddesired components, means for periodically and substantially decreasingthe current of said beam during said scanning which is at least twice'ashigh as the highestgenerated to develop coupled to said tube having afrequency charactothe frequency at which said beam current is decreasedfor deriving a signal which comprises said modulated carrier signal andwhich is substantially free of said undesired shading components. f

13. A signal-generating system comprising, a

cathode-ray signal-generating tube, afphotosensitive target electrode insaid tube, means for establishing a charge electrode in accordance witha signal to be generated, a source of beam current inl said tube, meansfor scanning. said target electrode during a scanning interval with saidbeam to generate desired signal components having frequencies thatextend over a range charge distribution on said target electrode andwhich also develops undesired shading compo- `nents with said desiredcomponents, means forA periodically' and substantially decreasing thecurrent of said beam during said scanning interval at a frequency whichis highest-frequency signal component generated to develop r. modulatedcarrier signal having a carrier-frequency component corresponding to thefrequency at which said beam current is decreased and having upper andlower sidebands of modulation components individuallyV representing saiddesired signal components, and frequencyresponsive means coupled to saidtube having a frequency characteristic related tothe frequency atwhichsaid beam current vis decreased for de substantially free of saidundesired shading components and which comriving a signal which isprises at least one of said sidebands of modula- 14. A signal-generatingsystem comprising, a

cathode-ray signal-generating tube, a photosenf sitive target electrodein said tube, ing components with said desired components,

means for periodically and substantially inter-A means for establishinga charge distribution on said target electrode in accordance with asignal to be trans-r mitted, a source means for scanning a scanninginterval of beam current in saidtube, said target electrode during withsaid beam to generate charge distribution on saidtarg'et electrode andto the white level of said image," and frequencyselective means coupledto said' tube having a' frequency characteristic related tothe frequencyat which said beam lcurrent is decreased forstabilizing said last-namedsignal components at a fixed level to derive -a signal which includessaid vcathode-ray signal-generating tube, a photosensitive targetelectrode in s aid tube, means for desired videofrequency signalcomponents and which is substantially free of said undesiredshadperiodicallyand sub which also develops undesired shading componentswith said desired components. Ymeans for tantially ldecreasing theduring said scanning interthe `highest-frequency signal componentgener-Jg ated todevelop a modulated carrier signal having 1 acarrier-frequency component correspondingtov I 'the frequency at whichsaid beam cinrent` is decreased and having upper and lower sidebands /omodulation components individually repre-l h s nting said desired signalcomponents, and establishing a charge distribution ln-said target 5 nleans 'including a band-pass nltercoupled to determined by the chargeconinterval at a frequency'. fl

distribution on said target' determined by the f at least as high as the8 Y 2,396,835 Y said tube having a frequency characteristic rethescanning frequency and which also develops lated to the frequency atwhich said beam curundesired shading components with said desired rentis decreased for deriving a signal which is components, means forperiodically and substansubstantially free of said undesired shadingcomtially decreasing the currentV of said beam durponents and whichcomprises at least one of said 5 ing said scanning interval at afrequency which sidebands of modulation components. is atleast as highas the highest-frequency sig- -15. A signal-generating systemcomprising, a nal component generated to develop a carrier cathode-raysignal-generating tube, a photosensignal modulated by said desiredsignal compositive target electrode in said tube, means for nents, andfrequency-responsive means coupled establishing a charge distribution onsaid target l0 to said tube having a frequency characteristic reeletrodein accordance with a signal to be translated to the frequency at whichsaid beam curmitted, a source of beam current in said tube, rent isdecreased for deriving a signal for transmeans for scanning said targetelectrode during mission which comprises4 modulation components ascanning interval with said beam to generate of said modulated carriersignal corresponding to desired signal components having frequencies )5said desired components and which is substanthat extend over a rangedetermined by the tially free of said undesired shading components.charge distribution on said target electrode and c ARTHUR V. LOUGHREN.

